The patent literature discloses DC electric arc furnaces having hearth or melt connectors for conducting current into a melt in a furnace's hearth to power an arc formed between the melt and an arcing electrode, example being the Bowman Pat. No. 3,789,127 and the Valchev et al U.S. Pat. No. 3,835,230. Insofar as is known, there has been no published disclosure of such hearth or melt connectors in any forms capable of being incorporated into DC furnaces which can be commercially made and used.
One practical form is disclosed by the presently allowed Stenkvist patent application Ser. No. 587,714, filed June 17, 1975 now U.S. Pat. No. 3,997,712 issued Dec. 14, 1976, and assigned to the assignee of the present application. There a hearth or melt connector is disclosed in the form of a unit which can be connected to the outside of an electric furnace, the furnace's hearth and the unit having openings through which a melt in the furnace can reach a hearth or melt conductor having a refractory enclosure forming a part of the unit. The construction is practical and can be incorporated into a DC electric arc furnace capable of commerical manufacture and use.
However, it has proven desirable to provide a DC arc furnace construction having a hearth or melt connector capable of commercial manufacture and use and which is simpler, less expensive and at least equally reliable as that disclosed by the Stenkvist application.
For commerical use, both AC and DC electric arc furnaces usually have a physical construction of the Herolt type described in detail by The Making, Shaping and Treating of Steel, 7th Edition, published by the U.S. Steel Corporation, reference being had to Chapter 16, 2 of this publication, this reference being hereby incorporated as a part of the present disclosure.
When operated as a DC furnace one or more of the hearth or melt connectors are used, the circuit being via the connector through the melt in the furnace's hearth and via the arc or arcs to the arcing electrode or electrodes.
Briefly stated, such a furnace comprises a steel shell supporting a lining of brick work, the bricks forming the bottom being outwardly stepped upwardly and covered with a layer of sintered granular refractory particles so as to form the hearth for containing the melt. The shell and brick lining forming the side wall are generally of cylindrical contour and extend upwardly to be covered by a roof through which the electrode or electrodes project downwardly to form an arc or arcs with metal charged in the hearth. At one side a tapping spout projects which is also formed by a steel shell, lined with brick work and covered by the sintered granular material so as to form in effect an extension of the hearth, the opposite side of the furnace having a slag opening. The furnace is vertical when operating but can be tilted either towards the tapping spout for tapping or towards the slag opening for deslagging.
As previously indicated, when operated as a DC furnace, a hearth or melt connector is required for forming an electrical connection with the melt in the hearth, the hearth being made of electrically non-conductive refractory materials as indicated, at least in the case of a commercial arc furnace of large capacity.